Shell Programming and Scripting

Use sar -r. The output is in pages available:
[quote
-r Reports unused memory pages and disk blocks:

freemem average pages avail-
able to user
processes.
[/quote]

You can check the pagesize on your system using the pagesize command and multiply that with the freemem to get the number of bytes free.

00:00:00 freemem freeswap
00:05:00 55231 3516920
00:10:00 55697 3523353
00:15:01 55820 3525048
00:20:00 55831 3516405
00:25:00 56004 3527199
00:30:00 56557 3536617
00:35:01 56658 3537858
00:40:00 56096 3519500
00:45:00 56544 3533461
00:50:00 57110 3538281
00:55:00 56966 3526247
01:00:00 57622 3543673
01:05:00 58208 3544007
01:10:01 58125 3541247
01:15:00 58566 3540626
01:20:00 58934 3553958
01:25:00 59873 3570670
01:30:01 60686 3584695
01:35:00 60732 3574105
01:40:00 61099 3586523
01:45:01 60866 3579143
01:50:00 60587 3564594
01:55:00 60976 3579511
02:00:00 60993 3578550
02:05:01 63150 3567562
02:10:00 62358 3540240
02:15:00 62561 3547554
02:20:00 62368 3541880
02:25:00 63065 3557576
02:30:01 63227 3559676
02:35:00 62705 3542004
02:40:00 58721 3471088
02:45:00 60885 3509944
02:50:00 60637 3505715
02:55:00 57674 3443795
03:00:01 62115 3532625
03:05:00 62327 3525089
03:10:00 62911 3541438

Average 59487 3540225

freemem command is not working in sun solaris

the above are the output from sar -r